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Einstein Toolkit Release

We are pleased to announce the fifth release (code name Lovelace (http://en.wikipedia.org/wiki/Ada_Lovelace) of the Einstein Toolkit, an open, community developed software infrastructure for relativistic astrophysics. This release includes beginning support for OpenCL (disabled by default). In addition, bug fixes accumulated since the previous release in October 2011 have been included.

The Einstein Toolkit is a collection of software components and tools for simulating and analyzing general relativistic astrophysical systems that builds on numerous software efforts in the numerical relativity community including CactusEinstein, the Carpet AMR infrastructure and the relativistic hydrodynamics code GRHydro (an updated and extended version of the public release of the Whisky code). The Cactus Framework is used as the underlying computational infrastructure providing large-scale parallelization, general computational components, and a model for collaborative, portable code development. The toolkit includes modules to build complete codes for simulating black hole spacetimes as well as systems governed by relativistic hydrodynamics.

The Einstein Toolkit uses a distributed software model and its different modules are developed, distributed, and supported either by the core team of Einstein Toolkit Maintainers, or by individual groups. Where modules are provided by external groups, the Einstein Toolkit Maintainers provide quality control for modules for inclusion in the toolkit and help coordinate support. The Einstein Toolkit Maintainers currently involve postdocs and faculty from five different institutions, and host weekly meetings that are open for anyone to join in.

Guiding principles for the design and implementation of the toolkit include: open, community-driven software development; well thought out and stable interfaces; separation of physics software from computational science infrastructure; provision of complete working production code; training and education for a new generation of researchers.

For more information about using or contributing to the Einstein Toolkit, or to join the Einstein Toolkit Consortium, please visit our web pages at http://einsteintoolkit.org.

The Einstein Toolkit contain over 170 regression test cases. On a large portion of the tested machines, all of these testsuites pass, using both MPI and OpenMP parallelization.

The changes between this and the previous release include:

– Accelerator Support

This release of the Einstein Toolkit adds support for GPUs and other accelerators. This support comprises three levels of abstraction, ranging from merely building and running both CUDA and OpenCL code, to automated code generation targeting GPUs instead of CPUs. As with any other programming paradigm (such as MPI or OpenMP), the performance benefits depend on the particular algorithms used and optimizations that are applied. In addition, the Simulation Factory greatly aids portability to a wide range of computing systems.

At the lowest level, Cactus now supports compiling, building, and running with either CUDA or OpenCL. CUDA is supported as new language in addition to C, C++, and Fortran; OpenCL is supported as an external library, and builds and executes compute kernels via run-time calls. Details are described in the user’s guide (for CUDA) and in thorn ExternalLibraries/OpenCL (for OpenCL).

Many accelerator platforms today separate between host memory and device memory, and require explicit copy or map operations to transfer data. An intermediate level of abstraction aids transferring grid variables between host and device, using schedule declarations to keep track of which data are needed where, and minimizing expensive data transfers. For OpenCL, there is a compact API to build and execute compute kernels at run time. Details are described in thorns CactusUtils/Accelerator and CactusUtils/OpenCLRunTime (with example parameter file).

Finally, the code generation system Kranc has been extended to be able to produce either C++ or OpenCL code, based on the infrastructure described above. This allows writing GPU code in a very high-level manner. However, it needs to be stated that the efficiency of the generated code depends on many variables, including e.g. the finite differencing stencil radius and the number of operations in the generated compute kernels. Non-trivial kernels typically require system-dependent tuning to execute efficiently, as GPUs and other accelerators generally show a rather unforgiving performance behavior. The thorns McLachlan/ML_WaveToy and McLachlan/ML_WaveToy_CL are examples, generated from the same Kranc script, showing the generated C++ and OpenCL code.

– SimFactory
– Machine database and optionlists updated due to system changes on HPC resources
– Simfactory’s capability of running the testsuites is properly tested on a lot of systems.
– IOUtil: checkpoint_dir is now steerable
– SphericalSurface: added functionality to name spherical surfaces
– Formaline: Support a “local repository” that collects all machine-local repositories
– TimerReport: Allow different timers on different processes
– WeylScal4: Enable use of LoopControl, and hence OpenMP
– EOS_Omni: use C interface for HDF5 to avoid needing Fortran HDF5 bindings
– EOSG_*: Support for the so-called ‘general EOS interface’ has been dropped from the Einstein Toolkit
– A new arrangement EinsteinExact has been added to the toolkit, providing a wide range of exact initial data, which will eventually replace the ‘Exact’ thorn.
– The *_O2 versions of McLachlan have been removed from the toolkit. This functionality is already provided by the regular McLachlan thorns now.
– A new thorn ADMMass has been added to the Einstein Toolkit, which can calculate approximations of the ADM mass using a finite surface or volume integral.
– The old library mechanism in Cactus (e.g. HDF5=yes) is now deprecated. Expect it to be removed in one of the next releases.
– The thorns ADM and LegoExcision are deprecated and will be removed in one of the next releases.
– GRHydro:
– use atmosphere integer mask instead of bitmask
– remove (now) unused old Tmunu interface
– Implemented enhanced PPM scheme by Colella & Sekora 2008, McCorquodale & Colella 2011. Can be activated by setting
use_enhanced_ppm = yes
– External Libraries: several updates and configuration improvements
– Cactus
– implement per-variable tolerances for Cactus testsuites, for long discussion, see ET ticket #114
– Allow arithmetic expression in ParameterSet: parameter files can now contain a limited set of expressions
– Handles requirements recursively
– A lot of smaller bug fixes
– McLachlan: Implement CCZ4 formulation
– CarpetMask: Keep track of the volume that is masked out
– CarpetLib: Define MPI reduction operators for complex numbers
– CarpetIOASCII: Add new “compact” output format
– Csrpet: Support accelerator data transfer
– CarpetRegrid2: Add periodic boundary conditions
– Simfactory
– Use OpenMP by default
– Make running testsuites using Simfactory possible
– Updated a lot of configurations

All repositories participating in this release carry a branch ET_2012_05 marking this release. These release branches will be updated if severe errors are found.

For more detailed information about the “Lovelace” release please read the long release announcement on the Einstein Toolkit web pages: http://einsteintoolkit.org/about/releases/ET_2012_05_announcement.php.

On behalf of the Einstein Toolkit Consortium: the “Lovelace” Release Team